Abstract

The Seebeck effect and the thermal diffusivity of La0.67Ca0.33MnO3−δ were investigated in the temperature range 35<T<300 K and in particular in the regime of the high magnetoresistance and maximum resistivity ρmax. We find a sign change of the thermoelectric power S(T) and a step in heat conductivity near ρmax which we attribute to a temperature‐induced metal–insulator transition at about 80 K, suggesting that the large giant magnetoresistance found in these substances is due to a field‐induced metal–insulator transition.